HyBi Working Group I. Fette
Internet-Draft Google, Inc.
Intended status: Standards Track October 17, 2010
Expires: April 20, 2011
The WebSocket protocoldraft-ietf-hybi-thewebsocketprotocol-03
Abstract
The WebSocket protocol enables two-way communication between a user
agent running untrusted code running in a controlled environment to a
remote host that has opted-in to communications from that code. The
security model used for this is the Origin-based security model
commonly used by Web browsers. The protocol consists of an initial
handshake followed by basic message framing, layered over TCP. The
goal of this technology is to provide a mechanism for browser-based
applications that need two-way communication with servers that does
not rely on opening multiple HTTP connections (e.g. using
XMLHttpRequest or <iframe>s and long polling).
Please send feedback to the hybi@ietf.org mailing list.
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Note
This draft is meant to reflect changes in direction in the HyBi
working group. There is not yet consensus on everything in this
draft. Specifically, details about the framing are still under
discussion, however this draft is much closer to what the group is
discussing than the previous draft. There have also been proposals
to change the handshake, so the handshake is also not in a final
form.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 20, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Internet-Draft The WebSocket protocol October 20101. Introduction1.1. Background
_This section is non-normative._
Historically, creating an instant messenger chat client as a Web
application has required an abuse of HTTP to poll the server for
updates while sending upstream notifications as distinct HTTP calls.
This results in a variety of problems:
o The server is forced to use a number of different underlying TCP
connections for each client: one for sending information to the
client, and a new one for each incoming message.
o The wire protocol has a high overhead, with each client-to-server
message having an HTTP header.
o The client-side script is forced to maintain a mapping from the
outgoing connections to the incoming connection to track replies.
A simpler solution would be to use a single TCP connection for
traffic in both directions. This is what the WebSocket protocol
provides. Combined with the WebSocket API, it provides an
alternative to HTTP polling for two-way communication from a Web page
to a remote server. [WSAPI]
The same technique can be used for a variety of Web applications:
games, stock tickers, multiuser applications with simultaneous
editing, user interfaces exposing server-side services in real time,
etc.
1.2. Protocol overview
_This section is non-normative._
The protocol has two parts: a handshake, and then the data transfer.
The handshake from the client looks as follows:
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GET /demo HTTP/1.1
Host: example.com
Connection: Upgrade
Sec-WebSocket-Key2: 12998 5 Y3 1 .P00
Sec-WebSocket-Protocol: sample
Upgrade: WebSocket
Sec-WebSocket-Key1: 4 @1 46546xW%0l 1 5
Origin: http://example.com
^n:ds[4U
The handshake from the server looks as follows:
HTTP/1.1 101 WebSocket Protocol Handshake
Upgrade: WebSocket
Connection: Upgrade
Sec-WebSocket-Origin: http://example.com
Sec-WebSocket-Location: ws://example.com/demo
Sec-WebSocket-Protocol: sample
8jKS'y:G*Co,Wxa-
The leading line from the client follows the Request-Line format.
The leading line from the server follows the Status-Line format. The
Request-Line and Status-Line productions are defined in the HTTP
specification.
After the leading line in both cases come an unordered ASCII case-
insensitive set of fields, one per line, that each match the
following non-normative ABNF: [RFC5234] [ANSI.X3-4.1986]
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field = 1*name-char colon [ space ] *any-char cr lf
colon = %x003A ; U+003A COLON (:)
space = %x0020 ; U+0020 SPACE
cr = %x000D ; U+000D CARRIAGE RETURN (CR)
lf = %x000A ; U+000A LINE FEED (LF)
name-char = %x0000-0009
/ %x000B-000C
/ %x000E-0039
/ %x003B-10FFFF
; a Unicode character other than
; U+000A LINE FEED (LF),
; U+000D CARRIAGE RETURN (CR),
; or U+003A COLON (:)
any-char = %x0000-0009 / %x000B-000C / %x000E-10FFFF
; a Unicode character other than
; U+000A LINE FEED (LF)
; or U+000D CARRIAGE RETURN (CR)
NOTE: The character set for the above ABNF is Unicode. The fields
themselves are encoded as UTF-8.
Lines that don't match the above production cause the connection to
be aborted.
Finally, after the last field, the client sends 10 bytes starting
with 0x0D 0x0A and followed by 8 random bytes, part of a challenge,
and the server sends 18 bytes starting with 0x0D 0x0A and followed by
16 bytes consisting of a challenge response. The details of this
challenge and other parts of the handshake are described in the next
section.
Once the client and server have both sent their handshakes, and if
the handshake was successful, then the data transfer part starts.
This is a two-way communication channel where each side can,
independently from the other, send data at will.
Clients and servers, after a successful handshake, transfer data back
and forth in conceptual units referred to in this specification as
"messages". A message is a complete unit of data at an application
level, with the expectation that many or most applications
implementing this protocol (such as web user agents) provide APIs in
terms of sending and receiving messages. The websocket message does
not necessarily correspond to a particular network layer framing, as
a fragmented message may be coalesced, or vice versa, e.g. by an
intermediary.
Data is sent on the wire in the form of frames that have an
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associated type. Broadly speaking, there are types for textual data,
which is interpreted as UTF-8 text, binary data (whose interpretation
is left up to the application), and control frames, which are not
intended to carry data for the application, but instead for protocol-
level signalling, such as to signal that the connection should be
closed. This version of the protocol defines six frame types and
leaves ten reserved for future use.
The WebSocket protocol uses this framing so that specifications that
use the WebSocket protocol can expose such connections using an
event-based mechanism instead of requiring users of those
specifications to implement buffering and piecing together of
messages manually.
1.3. Opening handshake
_This section is non-normative._
The opening handshake is intended to be compatible with HTTP-based
server-side software, so that a single port can be used by both HTTP
clients talking to that server and WebSocket clients talking to that
server. To this end, the WebSocket client's handshake appears to
HTTP servers to be a regular GET request with an Upgrade offer:
GET / HTTP/1.1
Upgrade: WebSocket
Connection: Upgrade
Fields in the handshake are sent by the client in a random order; the
order is not meaningful.
Additional fields are used to select options in the WebSocket
protocol. The only options available in this version are the
subprotocol selector, |Sec-WebSocket-Protocol|, and |Cookie|, which
can used for sending cookies to the server (e.g. as an authentication
mechanism). The |Sec-WebSocket-Protocol| request-header field can be
used to indicate what subprotocols (application-level protocols
layered over the WebSocket protocol) are acceptable to the client.
The server selects one of the acceptable protocols and echoes that
value in its handshake to indicate that it has selected that
protocol.
Sec-WebSocket-Protocol: chat superchat
The other fields in the handshake are all security-related. The
|Host| field is used to protect against DNS rebinding attacks and to
allow multiple domains to be served from one IP address.
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Host: example.com
The server includes the hostname in the |Sec-WebSocket-Location|
field of its handshake, so that both the client and the server can
verify that they agree on which host is in use.
The |Origin| field is used to protect against unauthorized cross-
origin use of a WebSocket server by scripts using the |WebSocket| API
in a Web browser. The server specifies which origin it is willing to
receive requests from by including a |Sec-WebSocket-Origin| field
with that origin. If multiple origins are authorized, the server
echoes the value in the |Origin| field of the client's handshake.
Origin: http://example.com
Finally, the server has to prove to the client that it received the
client's WebSocket handshake, so that the server doesn't accept
connections that are not WebSocket connections. This prevents an
attacker from tricking a WebSocket server by sending it carefully-
crafted packets using |XMLHttpRequest| or a |form| submission.
To prove that the handshake was received, the server has to take
three pieces of information and combine them to form a response. The
first two pieces of information come from the |Sec-WebSocket-Key1|
and |Sec-WebSocket-Key2| fields in the client handshake:
Sec-WebSocket-Key1: 18x 6]8vM;54 *(5: { U1]8 z [ 8
Sec-WebSocket-Key2: 1_ tx7X d < nw 334J702) 7]o}` 0
For each of these fields, the server has to take the digits from the
value to obtain a number (in this case 1868545188 and 1733470270
respectively), then divide that number by the number of spaces
characters in the value (in this case 12 and 10) to obtain a 32-bit
number (155712099 and 173347027). These two resulting numbers are
then used in the server handshake, as described below.
The counting of spaces is intended to make it impossible to smuggle
this field into the resource name; making this even harder is the
presence of _two_ such fields, and the use of a newline as the only
reliable indicator that the end of the key has been reached. The use
of random characters interspersed with the spaces and the numbers
ensures that the implementor actually looks for spaces and newlines,
instead of being treating any character like a space, which would
make it again easy to smuggle the fields into the path and trick the
server. Finally, _dividing_ by this number of spaces is intended to
make sure that even the most naive of implementations will check for
spaces, since if ther server does not verify that there are some
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spaces, the server will try to divide by zero, which is usually fatal
(a correct handshake will always have at least one space).
The third piece of information is given after the fields, in the last
eight bytes of the handshake, expressed here as they would be seen if
interpreted as UTF-8:
Tm[K T2u
The concatenation of the number obtained from processing the |Sec-
WebSocket-Key1| field, expressed as a big-endian 32 bit number, the
number obtained from processing the |Sec-WebSocket-Key2| field, again
expressed as a big-endian 32 bit number, and finally the eight bytes
at the end of the handshake, form a 128 bit string whose MD5 sum is
then used by the server to prove that it read the handshake.
The handshake from the server is much simpler than the client
handshake. The first line is an HTTP Status-Line, with the status
code 101 (the HTTP version and reason phrase aren't important):
HTTP/1.1 101 WebSocket Protocol Handshake
The fields follow. Two of the fields are just for compatibility with
HTTP:
Upgrade: WebSocket
Connection: Upgrade
Two of the fields are part of the security model described above,
echoing the origin and stating the exact host, port, resource name,
and whether the connection is expected to be encrypted:
Sec-WebSocket-Origin: http://example.com
Sec-WebSocket-Location: ws://example.com/
These fields are checked by the Web browser when it is acting as a
|WebSocket| client for scripted pages. A server that only handles
one origin and only serves one resource can therefore just return
hard-coded values and does not need to parse the client's handshake
to verify the correctness of the values.
Option fields can also be included. In this version of the protocol,
the main option field is |Sec-WebSocket-Protocol|, which indicates
the subprotocol that the server has selected. Web browsers verify
that the server included one of the values as was specified in the
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|WebSocket| constructor.A server that speaks multiple subprotocols
has to make sure it selects one based on the client's handshake and
specifies it in its handshake.
Sec-WebSocket-Protocol: chat
The server can also set cookie-related option fields to _set_
cookies, as in HTTP.
After the fields, the server sends the aforementioned MD5 sum, a 16
byte (128 bit) value, shown here as if interpreted as UTF-8:
fQJ,fN/4F4!~K~MH
This value depends on what the client sends, as described above. If
it doesn't match what the client is expecting, the client would
disconnect.
Having part of the handshake appear after the fields ensures that
both the server and the client verify that the connection is not
being interrupted by an HTTP intermediary such as a man-in-the-middle
cache or proxy.
1.4. Closing handshake
_This section is non-normative._
The closing handshake is far simpler than the opening handshake.
Either peer can send a control frame with data containing a specified
control sequence to begin the closing handshake. Upon receiving such
a frame, the other peer sends an identical frame in acknowledgement,
if it hasn't already sent one. Upon receiving _that_ control frame,
the first peer then closes the connection, safe in the knowledge that
no further data is forthcoming.
After sending a control frame indicating the connection should be
closed, a peer does not send any further data; after receiving a
control frame frame indicating the connection should be closed, a
peer discards any further data received.
It is safe for both peers to initiate this handshake simultaneously.
The closing handshake is intended to replace the TCP closing
handshake (FIN/ACK), on the basis that the TCP closing handshake is
not always reliable end-to-end, especially in the presence of man-in-
the-middle proxies and other intermediaries.
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Internet-Draft The WebSocket protocol October 20101.5. Design philosophy
_This section is non-normative._
The WebSocket protocol is designed on the principle that there should
be minimal framing (the only framing that exists is to make the
protocol frame-based instead of stream-based, and to support a
distinction between Unicode text and binary frames). It is expected
that metadata would be layered on top of WebSocket by the application
layer, in the same way that metadata is layered on top of TCP by the
application layer (HTTP).
Conceptually, WebSocket is really just a layer on top of TCP that
adds a Web "origin"-based security model for browsers; adds an
addressing and protocol naming mechanism to support multiple services
on one port and multiple host names on one IP address; layers a
framing mechanism on top of TCP to get back to the IP packet
mechanism that TCP is built on, but without length limits; and
reimplements the closing handshake in-band. Other than that, it adds
nothing. Basically it is intended to be as close to just exposing
raw TCP to script as possible given the constraints of the Web. It's
also designed in such a way that its servers can share a port with
HTTP servers, by having its handshake be a valid HTTP Upgrade
handshake also.
The protocol is intended to be extensible; future versions will
likely introduce a mechanism to compress data and might support
sending binary data.
1.6. Security model
_This section is non-normative._
The WebSocket protocol uses the origin model used by Web browsers to
restrict which Web pages can contact a WebSocket server when the
WebSocket protocol is used from a Web page. Naturally, when the
WebSocket protocol is used by a dedicated client directly (i.e. not
from a Web page through a Web browser), the origin model is not
useful, as the client can provide any arbitrary origin string.
This protocol is intended to fail to establish a connection with
servers of pre-existing protocols like SMTP or HTTP, while allowing
HTTP servers to opt-in to supporting this protocol if desired. This
is achieved by having a strict and elaborate handshake, and by
limiting the data that can be inserted into the connection before the
handshake is finished (thus limiting how much the server can be
influenced).
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It is similarly intended to fail to establish a connection when data
from other protocols, especially HTTP, is sent to a WebSocket server,
for example as might happen if an HTML |form| were submitted to a
WebSocket server. This is primarily achieved by requiring that the
server prove that it read the handshake, which it can only do if the
handshake contains the appropriate parts which themselves can only be
sent by a WebSocket handshake; in particular, fields starting with
|Sec-| cannot be set by an attacker from a Web browser, even when
using |XMLHttpRequest|.
1.7. Relationship to TCP and HTTP
_This section is non-normative._
The WebSocket protocol is an independent TCP-based protocol. Its
only relationship to HTTP is that its handshake is interpreted by
HTTP servers as an Upgrade request.
Based on the expert recommendation of the IANA, the WebSocket
protocol by default uses port 80 for regular WebSocket connections
and port 443 for WebSocket connections tunneled over TLS.
1.8. Establishing a connection
_This section is non-normative._
There are several options for establishing a WebSocket connection.
On the face of it, the simplest method would seem to be to use port
80 to get a direct connection to a WebSocket server. Port 80
traffic, however, will often be intercepted by man-in-the-middle HTTP
proxies, which can lead to the connection failing to be established.
The most reliable method, therefore, is to use TLS encryption and
port 443 to connect directly to a WebSocket server. This has the
advantage of being more secure; however, TLS encryption can be
computationally expensive.
When a connection is to be made to a port that is shared by an HTTP
server (a situation that is quite likely to occur with traffic to
ports 80 and 443), the connection will appear to the HTTP server to
be a regular GET request with an Upgrade offer. In relatively simple
setups with just one IP address and a single server for all traffic
to a single hostname, this might allow a practical way for systems
based on the WebSocket protocol to be deployed. In more elaborate
setups (e.g. with load balancers and multiple servers), a dedicated
set of hosts for WebSocket connections separate from the HTTP servers
is probably easier to manage.
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Internet-Draft The WebSocket protocol October 20101.9. Subprotocols using the WebSocket protocol
_This section is non-normative._
The client can request that the server use a specific subprotocol by
including the |Sec-Websocket-Protocol| field in its handshake. If it
is specified, the server needs to include the same field and one of
the selected subprotocol values in its response for the connection to
be established.
These subprotocol names do not need to be registered, but if a
subprotocol is intended to be implemented by multiple independent
WebSocket servers, potential clashes with the names of subprotocols
defined independently can be avoided by using names that contain the
domain name of the subprotocol's originator. For example, if Example
Corporation were to create a Chat subprotocol to be implemented by
many servers around the Web, they could name it "chat.example.com".
If the Example Organisation called their competing subprotocol
"example.org's chat protocol", then the two subprotocols could be
implemented by servers simultaneously, with the server dynamically
selecting which subprotocol to use based on the value sent by the
client.
Subprotocols can be versioned in backwards-incompatible ways by
changing the subprotocol name, eg. going from "bookings.example.net"
to "v2.bookings.example.net". These subprotocols would be considered
completely separate by WebSocket clients. Backwards-compatible
versioning can be implemented by reusing the same subprotocol string
but carefully designing the actual subprotocol to support this kind
of extensibility.
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Internet-Draft The WebSocket protocol October 20102. Conformance requirements
All diagrams, examples, and notes in this specification are non-
normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC2119. For
readability, these words do not appear in all uppercase letters in
this specification. [RFC2119]
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word
("must", "should", "may", etc) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps may
be implemented in any manner, so long as the end result is
equivalent. (In particular, the algorithms defined in this
specification are intended to be easy to follow, and not intended to
be performant.)
Implementations may impose implementation-specific limits on
otherwise unconstrained inputs, e.g. to prevent denial of service
attacks, to guard against running out of memory, or to work around
platform-specific limitations.
The conformance classes defined by this specification are user agents
and servers.
2.1. Terminology
*ASCII* shall mean the character-encoding scheme defined in
[ANSI.X3-4.1986].
*Converting a string to ASCII lowercase* means replacing all
characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER
A to LATIN CAPITAL LETTER Z) with the corresponding characters in the
range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL
LETTER Z).
Comparing two strings in an *ASCII case-insensitive* manner means
comparing them exactly, code point for code point, except that the
characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER
A to LATIN CAPITAL LETTER Z) and the corresponding characters in the
range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL
LETTER Z) are considered to also match.
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The term "URL" is used in this section in a manner consistent with
the terminology used in HTML, namely, to denote a string that might
or might not be a valid URI or IRI and to which certain error
handling behaviors will be applied when the string is parsed. [HTML]
When an implementation is required to _send_ data as part of the
WebSocket protocol, the implementation may delay the actual
transmission arbitrarily, e.g. buffering data so as to send fewer IP
packets.
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Internet-Draft The WebSocket protocol October 20103. WebSocket URLs3.1. Parsing WebSocket URLs
The steps to *parse a WebSocket URL's components* from a string /url/
are as follows. These steps return either a /host/, a /port/, a
/resource name/, and a /secure/ flag, or they fail.
1. If the /url/ string is not an absolute URL, then fail this
algorithm. [RFC3986] [RFC3987]
2. Resolve the /url/ string using the resolve a Web address
algorithm defined by the Web addresses specification, with the
URL character encoding set to UTF-8. [RFC3629] [RFC3986]
[RFC3987]
NOTE: It doesn't matter what it is resolved relative to, since
we already know it is an absolute URL at this point.
3. If /url/ does not have a <scheme> component whose value, when
converted to ASCII lowercase, is either "ws" or "wss", then fail
this algorithm.
4. If /url/ has a <fragment> component, then fail this algorithm.
5. If the <scheme> component of /url/ is "ws", set /secure/ to
false; otherwise, the <scheme> component is "wss", set /secure/
to true.
6. Let /host/ be the value of the <host> component of /url/,
converted to ASCII lowercase.
7. If /url/ has a <port> component, then let /port/ be that
component's value; otherwise, there is no explicit /port/.
8. If there is no explicit /port/, then: if /secure/ is false, let
/port/ be 80, otherwise let /port/ be 443.
9. Let /resource name/ be the value of the <path> component (which
might be empty) of /url/.
10. If /resource name/ is the empty string, set it to a single
character U+002F SOLIDUS (/).
11. If /url/ has a <query> component, then append a single U+003F
QUESTION MARK character (?) to /resource name/, followed by the
value of the <query> component.
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12. Return /host/, /port/, /resource name/, and /secure/.
3.2. Constructing WebSocket URLs
The steps to *construct a WebSocket URL* from a /host/, a /port/, a
/resource name/, and a /secure/ flag, are as follows:
1. Let /url/ be the empty string.
2. If the /secure/ flag is false, then append the string "ws://" to
/url/. Otherwise, append the string "wss://" to /url/.
3. Append /host/ to /url/.
4. If the /secure/ flag is false and port is not 80, or if the
/secure/ flag is true and port is not 443, then append the string
":" followed by /port/ to /url/.
5. Append /resource name/ to /url/.
6. Return /url/.
3.3. Valid WebSocket URLs
For a WebSocket URL to be considered valid, the following conditions
MUST hold.
o The /host/ must be ASCII-only (i.e. it must have been punycode-
encoded already if necessary, and MUST NOT contain any characters
above U+007E).
o The /origin/ must not contain characters in the range U+0041 to
U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
o The /resource name/ string must be a non-empty string of
characters in the range U+0021 to U+007E that starts with a U+002F
SOLIDUS character (/).
o The various strings in /protocols/ MUST all be non-empty strings
with characters in the range U+0021 to U+007E and MUST all be
unique.
Any WebSocket URLs not meeting the above criteria are considered
invalid, and a client MUST NOT attempt to make a connection to an
invalid WebSocket URL. A client SHOULD attempt to parse a URL
obtained from any external source (such as a web site or a user)
using the steps specified in Section 3.1 to obtain a valid WebSocket
URL, but MUST NOT attempt to connect with such an unparsed URL, and
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instead only use the parsed version and only if that version is
considered valid by the criteria above.
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Opcode: 4 bits
Defines the interpretation of the payload data
Payload length: 7 bits
The length of the payload: if 0-125, that is the payload length.
If 126, the following 2 bytes interpreted as a 16 bit unsigned
integer are the payload length. If 127, the following 8 bytes
interpreted as a 64-bit unsigned integer (the high bit must be 0)
are the payload length. Multibyte length quantities are expressed
in network byte order. The payload length is the length of the
Extension data + the length of the Application Data. The length
of the Extension data may be zero, in which case the Payload
length is the length of the Application data.
Extension data: n bytes
The extension data is 0 bytes unless there is a reserved op-code
or reserved bit present in the frame which indicates an extension
has been negotiated. Any extension MUST specify the length of the
extension data, or how that length may be calculated, and its use
MUST be negotiated during the handshake. If present, the
extension data is included in the total payload length.
Application data: n bytes
Arbitrary application data, taking up the remainder of the frame
after any extension data. The length of the Application data is
equal to the payload length minus the length of the Extension
data.
The base framing protocol is formally defined by the following ABNF
[RFC5234]:
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o A fragmented message consists of a single frame with the MORE bit
set and an opcode other than 0, followed by zero or more frames
with the MORE bit set and the opcode set to 0, and terminated by a
single frame with the MORE bit clear and an opcode of 0. Its
content is the concatenation of the application data from each of
those frames in order.
o _Note: There is an open question as to whether control frames be
interjected in the middle of a fragmented message. If so, it must
be decided whether they be fragmented (which would require keeping
a stack of "in-progress" messages)._
o A sender MAY create fragments of any size for non control
messages.
o Clients and servers MUST support receiving both fragmented and
unfragmented messages.
o An intermediary MAY change the fragmentation of a message if the
message uses only opcode and reserved bit values known to the
intermediary.
4.4. Control Frames
Control frames have opcodes of 0x01 (Close), 0x02 (Ping), or 0x03
(Pong). Control frames are used to communicate state about the
websocket.
All control frames MUST be 125 bytes or less in length and MUST NOT
be fragmented.
4.4.1. Close
The Close message contains an opcode of 0x01.
The application MUST NOT send any more data messages after sending a
close message.
A recevied close message is deemed to be an acknowledgement if the
message body matches the body of a close message previously sent by
the receiver. Otherwise the close message is a close initiated by
the sender.
Upon receipt of an initiated close the endpoint MUST send a close
acknowledgment. It should do so as soon as is practical.
The websocket is considered fully closed when an endpoint has either
received a close acknowledgment or sent a close acknowledgment.
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The Ping message contains an opcode of 0x02.
Upon receipt of a Ping message, an endpoint MUST send a Pong message
in response. It SHOULD do so as soon as is practical. The message
bodies of the Ping and Pong MUST be the same.
4.4.3. Pong
The Pong message contains an opcode of 0x03.
Upon receipt of a Ping message, an endpoint MUST send a Pong message
in response. It SHOULD do so as soon as is practical. The message
bodies of the Ping and Pong MUST be the same.
4.5. Data Frames
All frame types not listed in Section 4.4 are data frames, which
transport application-layer data. The opcode determines the
interpretation of the application data:
Text
The payload data is text data encoded as UTF-8.
Binary
The payload data is arbitrary binary data whose interpretation is
solely up to the application layer.
4.6. Examples
_This section is non-normative._
o A single-frame text message
* 0x04 0x05 "Hello"
o A fragmented text message
* 0x84 0x03 "Hel"
* 0x00 0x02 "lo"
o Ping request and response
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* 0x02 0x05 "Hello"
* 0x03 0x05 "Hello"
o 256 bytes binary message in a single frame
* 0x05 0x7E 0x0100 [256 bytes of binary data]
o 64KiB binary message in a single frame
* 0x05 0x7F 0x0000000000010000 [65536 bytes of binary data]
4.7. Extensibility
The protocol is designed to allow for extensions, which will add
capabilities to the base protocols. The endpoints of a connection
MUST negotiate the use of any extensions during the handshake. This
specification provides opcodes 0x6 through 0xF, the extension data
field, and the frame-rsv1, frame-rsv2, frame-rsv3, and frame-rsv4
bits of the frame header for use by extensions. Below are some
anticipated uses of extensions. This list is neither complete nor
proscriptive.
o Extension data may be placed in the payload before the application
data.
o Reserved bits can be allocated for per-frame needs.
o Reserved opcode values can be defined.
o Reserved bits can be allocated to the opcode field if more opcode
values are needed.
o A reserved bit or an "extension" opcode can be defined which
allocates additional bits out of the payload area to define larger
opcodes or more per-frame bits.
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User agents running in controlled environments, e.g. browsers on
mobile handsets tied to specific carriers, may offload the management
of the connection to another agent on the network. In such a
situation, the user agent for the purposes of conformance is
considered to include both the handset software and any such agents.
When the user agent is to *establish a WebSocket connection* to a
host /host/, on a port /port/, from an origin whose ASCII
serialization is /origin/, with a flag /secure/, with a string giving
a /resource name/, with a (possibly empty) list of strings giving the
/protocols/, and optionally with a /defer cookies/ flag, it must run
the following steps. [ORIGIN]
1. Verify that the WebSocket URL and its components are valid
according to Section 3.3. If any of the requirements are not
met, the client MUST fail the WebSocket connection and abort
these steps.
2. If the user agent already has a WebSocket connection to the
remote host (IP address) identified by /host/, even if known by
another name, wait until that connection has been established or
for that connection to have failed. If multiple connections to
the same IP address are attempted simultaneously, the user agent
must serialize them so that there is no more than one connection
at a time running through the following steps.
If the user agent cannot determine the IP address of the remote
host (for example because all communication is being done
through a proxy server that performs DNS queries itself), then
the user agent must assume for the purposes of this step that
each host name refers to a distinct remote host, but should
instead limit the total number of simultaneous connections that
are not established to a reasonably low number (e.g., in a Web
browser, to the number of tabs the user has open).
NOTE: This makes it harder for a script to perform a denial of
service attack by just opening a large number of WebSocket
connections to a remote host. A server can further reduce the
load on itself when attacked by making use of this by pausing
before closing the connection, as that will reduce the rate at
which the client reconnects.
NOTE: There is no limit to the number of established WebSocket
connections a user agent can have with a single remote host.
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Servers can refuse to connect users with an excessive number of
connections, or disconnect resource-hogging users when suffering
high load.
3. _Connect_: If the user agent is configured to use a proxy when
using the WebSocket protocol to connect to host /host/ and/or
port /port/, then connect to that proxy and ask it to open a TCP
connection to the host given by /host/ and the port given by
/port/.
EXAMPLE: For example, if the user agent uses an HTTP proxy
for all traffic, then if it was to try to connect to port 80
on server example.com, it might send the following lines to
the proxy server:
CONNECT example.com:80 HTTP/1.1
Host: example.com
If there was a password, the connection might look like:
CONNECT example.com:80 HTTP/1.1
Host: example.com
Proxy-authorization: Basic ZWRuYW1vZGU6bm9jYXBlcyE=
Otherwise, if the user agent is not configured to use a proxy,
then open a TCP connection to the host given by /host/ and the
port given by /port/.
NOTE: Implementations that do not expose explicit UI for
selecting a proxy for WebSocket connections separate from other
proxies are encouraged to use a SOCKS proxy for WebSocket
connections, if available, or failing that, to prefer the proxy
configured for HTTPS connections over the proxy configured for
HTTP connections.
For the purpose of proxy autoconfiguration scripts, the URL to
pass the function must be constructed from /host/, /port/,
/resource name/, and the /secure/ flag using the steps to
construct a WebSocket URL.
NOTE: The WebSocket protocol can be identified in proxy
autoconfiguration scripts from the scheme ("ws:" for unencrypted
connections and "wss:" for encrypted connections).
4. If the connection could not be opened, then fail the WebSocket
connection and abort these steps.
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5. If /secure/ is true, perform a TLS handshake over the
connection. If this fails (e.g. the server's certificate could
not be verified), then fail the WebSocket connection and abort
these steps. Otherwise, all further communication on this
channel must run through the encrypted tunnel. [RFC2246]
User agents must use the Server Name Indication extension in the
TLS handshake. [RFC4366]
6. Send the UTF-8 string "GET" followed by a UTF-8-encoded U+0020
SPACE character to the remote side (the server).
Send the /resource name/ value, encoded as UTF-8.
Send another UTF-8-encoded U+0020 SPACE character, followed by
the UTF-8 string "HTTP/1.1", followed by a UTF-8-encoded U+000D
CARRIAGE RETURN U+000A LINE FEED character pair (CRLF).
7. Let /fields/ be an empty list of strings.
8. Add the string "Upgrade: WebSocket" to /fields/.
9. Add the string "Connection: Upgrade" to /fields/.
10. Let /hostport/ be an empty string.
11. Append the /host/ value, converted to ASCII lowercase, to
/hostport/.
12. If /secure/ is false, and /port/ is not 80, or if /secure/ is
true, and /port/ is not 443, then append a U+003A COLON
character (:) followed by the value of /port/, expressed as a
base-ten integer, to /hostport/.
13. Add the string consisting of the concatenation of the string
"Host:", a U+0020 SPACE character, and /hostport/, to /fields/.
14. Add the string consisting of the concatenation of the string
"Origin:", a U+0020 SPACE character, and the /origin/ value, to
/fields/.
15. Add the string "Sec-WebSocket-Draft: 2" to /fields/.
16. If there is no /protocols/, then skip this step.
Otherwise, generate the acceptable protocol string by joining
each protocol in /protocols/ using a U+0020 SPACE character.
Add the string consisting of the concatenation of the string
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"Sec-WebSocket-Protocol:", a U+0020 SPACE character, and the
acceptable protocol string generated above, to /fields/.
17. If the client has any cookies that would be relevant to a
resource accessed over HTTP, if /secure/ is false, or HTTPS, if
it is true, on host /host/, port /port/, with /resource name/ as
the path (and possibly query parameters), then add to /fields/
any HTTP headers that would be appropriate for that information.
[RFC2616] [RFC2109] [RFC2965]
This includes "HttpOnly" cookies (cookies with the http-only-
flag set to true); the WebSocket protocol is not considered a
non-HTTP API for the purpose of cookie processing.
18. When one or more HTTP headers are to be added to /fields/ for
this step, each header must be added separately, and each header
must be added as one entry consisting of the header's name in
its canonical case, followed by a U+003A COLON character (:) and
a U+0020 SPACE character, followed by the value with no use of
continuation lines (e.g. containing no U+000A LINE FEED
characters.)
19. Let /spaces_1/ be a random integer from 1 to 12 inclusive.
Let /spaces_2/ be a random integer from 1 to 12 inclusive.
EXAMPLE: For example, 5 and 9.
20. Let /max_1/ be the largest integer not greater than
4,294,967,295 divided by /spaces_1/.
Let /max_2/ be the largest integer not greater than
4,294,967,295 divided by /spaces_2/.
EXAMPLE: Continuing the example, 858,993,459 and 477,218,588.
21. Let /number_1/ be a random integer from 0 to /max_1/ inclusive.
Let /number_2/ be a random integer from 0 to /max_2/ inclusive.
EXAMPLE: For example, 777,007,543 and 114,997,259.
22. Let /product_1/ be the result of multiplying /number_1/ and
/spaces_1/ together.
Let /product_2/ be the result of multiplying /number_2/ and
/spaces_2/ together.
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EXAMPLE: Continuing the example, 3,885,037,715 and
1,034,975,331.
23. Let /key_1/ be a string consisting of /product_1/, expressed in
base ten using the numerals in the range U+0030 DIGIT ZERO (0)
to U+0039 DIGIT NINE (9).
Let /key_2/ be a string consisting of /product_2/, expressed in
base ten using the numerals in the range U+0030 DIGIT ZERO (0)
to U+0039 DIGIT NINE (9).
EXAMPLE: Continuing the example, "3885037715" and "1034975331".
24. Insert between one and twelve random characters from the ranges
U+0021 to U+002F and U+003A to U+007E into /key_1/ at random
positions.
Insert between one and twelve random characters from the ranges
U+0021 to U+002F and U+003A to U+007E into /key_2/ at random
positions.
NOTE: This corresponds to random printable ASCII characters
other than the digits and the U+0020 SPACE character.
EXAMPLE: Continuing the example, this could lead to "P388O503D&
ul7{K%gX(%715" and "1N?|kUT0or3o4I97N5-S3O31".
25. Insert /spaces_1/ U+0020 SPACE characters into /key_1/ at random
positions other than the start or end of the string.
Insert /spaces_2/ U+0020 SPACE characters into /key_2/ at random
positions other than the start or end of the string.
EXAMPLE: Continuing the example, this could lead to "P388 O503D&
ul7 {K%gX( %7 15" and "1 N ?|k UT0or 3o 4 I97N 5-S3O 31".
26. Add the string consisting of the concatenation of the string
"Sec-WebSocket-Key1:", a U+0020 SPACE character, and the /key_1/
value, to /fields/.
Add the string consisting of the concatenation of the string
"Sec-WebSocket-Key2:", a U+0020 SPACE character, and the /key_2/
value, to /fields/.
27. For each string in /fields/, in a random order: send the string,
encoded as UTF-8, followed by a UTF-8-encoded U+000D CARRIAGE
RETURN U+000A LINE FEED character pair (CRLF). It is important
that the fields be output in a random order so that servers not
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depend on the particular order used by any particular client.
28. Send a UTF-8-encoded U+000D CARRIAGE RETURN U+000A LINE FEED
character pair (CRLF).
29. Let /key_3/ be a string consisting of eight random bytes (or
equivalently, a random 64 bit unsigned integer encoded in big-
endian order).
EXAMPLE: For example, 0x47 0x30 0x22 0x2D 0x5A 0x3F 0x47 0x58.
30. Send /key_3/ to the server.
31. Read bytes from the server until either the connection closes,
or a 0x0A byte is read. Let /field/ be these bytes, including
the 0x0A byte.
If /field/ is not at least seven bytes long, or if the last two
bytes aren't 0x0D and 0x0A respectively, or if /field/ contains
any 0x0D bytes other than the penultimate byte, or if /field/
does not contain at least two 0x20 bytes, then _fail the
WebSocket connection_ and abort these steps.
User agents may apply a timeout to this step, failing the
WebSocket connection if the server does not send back data in a
suitable time period.
32. Let /code/ be the substring of /field/ that starts from the byte
after the first 0x20 byte, and ends with the byte before the
second 0x20 byte.
33. If /code/, interpreted as UTF-8, is "101", then move to the next
step.
If /code/, interpreted as UTF-8, is "407", then either close the
connection and jump back to step 2, providing appropriate
authentication information, or fail the WebSocket connection.
407 is the code used by HTTP meaning "Proxy Authentication
Required". User agents that support proxy authentication must
interpret the response as defined by HTTP (e.g. to find and
interpret the |Proxy-Authenticate| header).
Otherwise, fail the WebSocket connection and abort these steps.
34. Let /fields/ be a list of name-value pairs, initially empty.
35. _Field_: Let /name/ and /value/ be empty byte arrays.
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36. Read a byte from the server.
If the connection closes before this byte is received, then fail
the WebSocket connection and abort these steps.
Otherwise, handle the byte as described in the appropriate entry
below:
-> If the byte is 0x0D (UTF-8 CR)
If the /name/ byte array is empty, then jump to the fields
processing step. Otherwise, fail the WebSocket connection
and abort these steps.
-> If the byte is 0x0A (UTF-8 LF)
Fail the WebSocket connection and abort these steps.
-> If the byte is 0x3A (UTF-8 :)
Move on to the next step.
-> If the byte is in the range 0x41 to 0x5A (UTF-8 A-Z)
Append a byte whose value is the byte's value plus 0x20 to
the /name/ byte array and redo this step for the next byte.
-> Otherwise
Append the byte to the /name/ byte array and redo this step
for the next byte.
NOTE: This reads a field name, terminated by a colon, converting
upper-case letters in the range A-Z to lowercase, and aborting
if a stray CR or LF is found.
37. Let /count/ equal 0.
NOTE: This is used in the next step to skip past a space
character after the colon, if necessary.
38. Read a byte from the server and increment /count/ by 1.
If the connection closes before this byte is received, then fail
the WebSocket connection and abort these steps.
Otherwise, handle the byte as described in the appropriate entry
below:
-> If the byte is 0x20 (UTF-8 space) and /count/ equals 1
Ignore the byte and redo this step for the next byte.
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-> If the byte is 0x0D (UTF-8 CR)
Move on to the next step.
-> If the byte is 0x0A (UTF-8 LF)
Fail the WebSocket connection and abort these steps.
-> Otherwise
Append the byte to the /value/ byte array and redo this step
for the next byte.
NOTE: This reads a field value, terminated by a CRLF, skipping
past a single space after the colon if there is one.
39. Read a byte from the server.
If the connection closes before this byte is received, or if the
byte is not a 0x0A byte (UTF-8 LF), then fail the WebSocket
connection and abort these steps.
NOTE: This skips past the LF byte of the CRLF after the field.
40. Append an entry to the /fields/ list that has the name given by
the string obtained by interpreting the /name/ byte array as a
UTF-8 byte stream and the value given by the string obtained by
interpreting the /value/ byte array as a UTF-8 byte stream.
41. Return to the "Field" step above.
42. _Fields processing_: Read a byte from the server.
If the connection closes before this byte is received, or if the
byte is not a 0x0A byte (UTF-8 LF), then fail the WebSocket
connection and abort these steps.
NOTE: This skips past the LF byte of the CRLF after the blank
line after the fields.
43. Let the /list of cookies/ be empty.
44. If there is not exactly one entry in the /fields/ list whose
name is "upgrade", or if there is not exactly one entry in the
/fields/ list whose name is "connection", or if there is not
exactly one entry in the /fields/ list whose name is "sec-
websocket-origin", or if there is not exactly one entry in the
/fields/ list whose name is "sec-websocket-location", or if the
/protocol/ was specified but there is not exactly one entry in
the /fields/ list whose name is "sec-websocket-protocol", or if
there are any entries in the /fields/ list whose names are the
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empty string, then fail the WebSocket connection and abort these
steps. Otherwise, handle each entry in the /fields/ list as
follows:
-> If the entry's name is "upgrade"
If the value, converted to ASCII lowercase, is not exactly
equal to the string "websocket", then fail the WebSocket
connection and abort these steps.
-> If the entry's name is "connection"
If the value, converted to ASCII lowercase, is not exactly
equal to the string "upgrade", then fail the WebSocket
connection and abort these steps.
-> If the entry's name is "sec-websocket-origin"
If the value is not exactly equal to /origin/, then fail the
WebSocket connection and abort these steps. [ORIGIN]
-> If the entry's name is "sec-websocket-location"
If the value is not exactly equal to a string obtained from
the steps to construct a WebSocket URL from /host/, /port/,
/resource name/, and the /secure/ flag, then fail the
WebSocket connection and abort these steps.
-> If the entry's name is "sec-websocket-protocol"
If there was a /protocols/ string specified, and the value is
not exactly equal to one of the items in /protocols/, then
fail the WebSocket connection and abort these steps. (If no
/protocols/ was specified, the field is ignored.)
-> If the entry's name is "set-cookie" or "set-cookie2" or
another cookie-related field name
If the relevant specification is supported by the user agent,
add the cookie, interpreted as defined by the appropriate
specification, to the /list of cookies/, with the resource
being the one with the host /host/, the port /port/, the path
(and possibly query parameters) /resource name/, and the
scheme |http| if /secure/ is false and |https| if /secure/ is
true. [RFC2109] [RFC2965]
If the relevant specification is not supported by the user
agent, then the field must be ignored.
The cookies added to the /list of cookies/ are discarded if
the connection fails to be established. Only if and when the
connection is established do the cookies actually get
applied.
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-> Any other name
Ignore it.
45. Let /challenge/ be the concatenation of /number_1/, expressed as
a big-endian 32 bit integer, /number_2/, expressed as a big-
endian 32 bit integer, and the eight bytes of /key_3/ in the
order they were sent on the wire.
EXAMPLE: Using the examples given earlier, this leads to the 16
bytes 0x2E 0x50 0x31 0xB7 0x06 0xDA 0xB8 0x0B 0x47 0x30 0x22
0x2D 0x5A 0x3F 0x47 0x58.
46. Let /expected/ be the MD5 fingerprint of /challenge/ as a big-
endian 128 bit string. [RFC1321]
EXAMPLE: Using the examples given earlier, this leads to the 16
bytes 0x30 0x73 0x74 0x33 0x52 0x6C 0x26 0x71 0x2D 0x32 0x5A
0x55 0x5E 0x77 0x65 0x75. In UTF-8, these bytes correspond to
the string "0st3Rl&q-2ZU^weu".
47. Read sixteen bytes from the server. Let /reply/ be those bytes.
If the connection closes before these bytes are received, then
fail the WebSocket connection and abort these steps.
48. If /reply/ does not exactly equal /expected/, then fail the
WebSocket connection and abort these steps.
49. If the /defer cookies/ flag is not set, apply the cookies in the
/list of cookies/.
50. The *WebSocket connection is established*. Now the user agent
must send and receive to and from the connection as described in
the next section.
51. If the /defer cookies/ flag is set, store the /list of cookies/
for use by the component that invoked this algorithm.
Where the algorithm above requires that a user agent fail the
WebSocket connection, the user agent may first read an arbitrary
number of further bytes from the connection (and then discard them)
before actually *failing the WebSocket connection*. Similarly, if a
user agent can show that the bytes read from the connection so far
are such that there is no subsequent sequence of bytes that the
server can send that would not result in the user agent being
required to *fail the WebSocket connection*, the user agent may
immediately *fail the WebSocket connection* without waiting for those
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bytes.
NOTE: The previous paragraph is intended to make it conforming for
user agents to implement the algorithm in subtlely different ways
that are equivalent in all ways except that they terminate the
connection at earlier or later points. For example, it enables an
implementation to buffer the entire handshake response before
checking it, or to verify each field as it is received rather than
collecting all the fields and then checking them as a block.
When the user agent is to "apply the cookies" in a /list of cookies/,
it must handle each cookie in the /list of cookies/ as defined by the
appropriate specification. [RFC2109] [RFC2965]
5.2. Server-side requirements
_This section only applies to servers._
Servers may offload the management of the connection to other agents
on the network, for example load balancers and reverse proxies. In
such a situation, the server for the purposes of conformance is
considered to include all parts of the server-side infrastructure
from the first device to terminate the TCP connection all the way to
the server that processes requests and sends responses.
EXAMPLE: For example, a data center might have a server that responds
to Web Socket requests with an appropriate handshake, and then passes
the connection to another server to actually process the data frames.
For the purposes of this specification, the "server" is the
combination of both computers.
5.2.1. Reading the client's opening handshake
When a client starts a WebSocket connection, it sends its part of the
opening handshake. The server must parse at least part of this
handshake in order to obtain the necessary information to generate
the server part of the handshake.
The client handshake consists of the following parts. If the server,
while reading the handshake, finds that the client did not send a
handshake that matches the description below, the server should abort
the WebSocket connection.
1. The three-character UTF-8 string "GET".
2. A UTF-8-encoded U+0020 SPACE character (0x20 byte).
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3. A string consisting of all the bytes up to the next UTF-8-encoded
U+0020 SPACE character (0x20 byte). The result of decoding this
string as a UTF-8 string is the name of the resource requested by
the server. If the server only supports one resource, then this
can safely be ignored; the client verifies that the right
resource is supported based on the information included in the
server's own handshake. The resource name will begin with U+002F
SOLIDUS character (/) and will only include characters in the
range U+0021 to U+007E.
4. A string of bytes terminated by a UTF-8-encoded U+000D CARRIAGE
RETURN U+000A LINE FEED character pair (CRLF). All the
characters from the second 0x20 byte up to the first 0x0D 0x0A
byte pair in the data from the client can be safely ignored. (It
will probably be the string "HTTP/1.1".)
5. A series of fields.
Each field is terminated by a UTF-8-encoded U+000D CARRIAGE
RETURN U+000A LINE FEED character pair (CRLF). The end of the
fields is denoted by the terminating CRLF pair being followed
immediately by another CRLF pair.
NOTE: In other words, the fields start with the first 0x0D 0x0A
byte pair, end with the first 0x0D 0x0A 0x0D 0x0A byte sequence,
and are separate from each other by 0x0D 0x0A byte pairs.
The fields are encoded as UTF-8.
Each field consists of a name, consisting of one or more
characters in the ranges U+0021 to U+0039 and U+003B to U+007E,
followed by a U+003A COLON character (:) and a U+0020 SPACE
character, followed by zero or more characters forming the value.
The expected field names, the meaning of their corresponding
values, and the processing servers are required to apply to those
fields, are described below, after the description of the client
handshake.
6. After the first 0x0D 0x0A 0x0D 0x0A byte sequence, indicating the
end of the fields, the client sends eight random bytes. These
are used in constructing the server handshake.
The expected field names, and the meaning of their corresponding
values, are as follows. Field names must be compared in an ASCII
case-insensitive manner.
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|Upgrade|
Invariant part of the handshake. Will always have a value that is
an ASCII case-insensitive match for the string "WebSocket".
Can be safely ignored, though the server should abort the
WebSocket connection if this field is absent or has a different
value, to avoid vulnerability to cross-protocol attacks.
|Connection|
Invariant part of the handshake. Will always have a value that is
an ASCII case-insensitive match for the string "Upgrade".
Can be safely ignored, though the server should abort the
WebSocket connection if this field is absent or has a different
value, to avoid vulnerability to cross-protocol attacks.
|Host|
The value gives the hostname that the client intended to use when
opening the WebSocket. It would be of interest in particular to
virtual hosting environments, where one server might serve
multiple hosts, and might therefore want to return different data.
Can be safely ignored, though the server should abort the
WebSocket connection if this field is absent or has a value that
does not match the server's host name, to avoid vulnerability to
cross-protocol attacks and DNS rebinding attacks.
|Origin|
The value gives the scheme, hostname, and port (if it's not the
default port for the given scheme) of the page that asked the
client to open the WebSocket. It would be interesting if the
server's operator had deals with operators of other sites, since
the server could then decide how to respond (or indeed, _whether_
to respond) based on which site was requesting a connection.
[ORIGIN]
Can be safely ignored, though the server should abort the
WebSocket connection if this field is absent or has a value that
does not match one of the origins the server is expecting to
communicate with, to avoid vulnerability to cross-protocol attacks
and cross-site scripting attacks.
|Sec-WebSocket-Protocol|
The value gives the name of a subprotocol that the client is
intending to select. It would be interesting if the server
supports multiple protocols or protocol versions.
Can be safely ignored, though the server may abort the WebSocket
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connection if the field is absent but the conventions for
communicating with the server are such that the field is expected;
and the server should abort the WebSocket connection if the field
has a value that does not match one of the subprotocols that the
server supports, to avoid integrity errors once the connection is
established.
|Sec-WebSocket-Key1|
|Sec-WebSocket-Key2|
The values provide the information required for computing the
server's handshake, as described in the next section.
|Sec-WebSocket-Draft|
The value provides the version of this draft protocol that the
client is attempting to establish a connection using. If this
value is not equal to a version of the draft protocol that the
server understands, the server MUST abort the WebSocket
connection.
Other fields
Other fields can be used, such as "Cookie", for authentication
purposes. Their semantics are equivalent to the semantics of the
HTTP headers with the same names.
Unrecognized fields can be safely ignored, and are probably either
the result of intermediaries injecting fields unrelated to the
operation of the WebSocket protocol, or clients that support future
versions of the protocol offering options that the server doesn't
support.
5.2.2. Sending the server's opening handshake
When a client establishes a WebSocket connection to a server, the
server must run the following steps.
1. If the server supports encryption, perform a TLS handshake over
the connection. If this fails (e.g. the client indicated a host
name in the extended client hello "server_name" extension that
the server does not host), then close the connection; otherwise,
all further communication for the connection (including the
server handshake) must run through the encrypted tunnel.
[RFC2246]
2. Establish the following information:
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/host/
The host name or IP address of the WebSocket server, as it is
to be addressed by clients. The host name must be punycode-
encoded if necessary. If the server can respond to requests
to multiple hosts (e.g. in a virtual hosting environment),
then the value should be derived from the client's handshake,
specifically from the "Host" field. The /host/ value must be
lowercase (not containing characters in the range U+0041
LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z).
/port/
The port number on which the server expected and/or received
the connection.
/resource name/
An identifier for the service provided by the server. If the
server provides multiple services, then the value should be
derived from the resource name given in the client's
handshake.
/secure flag/
True if the connection is encrypted or if the server expected
it to be encrypted; false otherwise.
/origin/
The ASCII serialization of the origin that the server is
willing to communicate with, converted to ASCII lowercase.
If the server can respond to requests from multiple origins
(or indeed, all origins), then the value should be derived
from the client's handshake, specifically from the "Origin"
field. [ORIGIN]
/subprotocol/
Either null, or a string representing the subprotocol the
server is ready to use. If the server supports multiple
subprotocols, then the value should be derived from the
client's handshake, specifically by selecting one of the
values from the "Sec-WebSocket-Protocol" field. The absence
of such a field is equivalent to the null value. The empty
string is not the same as the null value for these purposes.
/key_1/
The value of the "Sec-WebSocket-Key1" field in the client's
handshake.
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/key_2/
The value of the "Sec-WebSocket-Key2" field in the client's
handshake.
/key_3/
The eight random bytes sent after the first 0x0D 0x0A 0x0D
0x0A sequence in the client's handshake.
3. Let /location/ be the string that results from constructing a
WebSocket URL from /host/, /port/, /resource name/, and /secure
flag/.
4. Let /key-number_1/ be the digits (characters in the range U+0030
DIGIT ZERO (0) to U+0039 DIGIT NINE (9)) in /key_1/, interpreted
as a base ten integer, ignoring all other characters in /key_1/.
Let /key-number_2/ be the digits (characters in the range U+0030
DIGIT ZERO (0) to U+0039 DIGIT NINE (9)) in /key_2/, interpreted
as a base ten integer, ignoring all other characters in /key_2/.
EXAMPLE: For example, assume that the client handshake was:
GET / HTTP/1.1
Connection: Upgrade
Host: example.com
Upgrade: WebSocket
Sec-WebSocket-Key1: 3e6b263 4 17 80
Origin: http://example.com
Sec-WebSocket-Key2: 17 9 G`ZD9 2 2b 7X 3 /r90
WjN}|M(6
The /key-number_1/ would be the number 3,626,341,780, and the
/key-number_2/ would be the number 1,799,227,390.
In this example, incidentally, /key_3/ is "WjN}|M(6", or 0x57
0x6A 0x4E 0x7D 0x7C 0x4D 0x28 0x36.
5. Let /spaces_1/ be the number of U+0020 SPACE characters in
/key_1/.
Let /spaces_2/ be the number of U+0020 SPACE characters in
/key_2/.
If either /spaces_1/ or /spaces_2/ is zero, then abort the
WebSocket connection. This is a symptom of a cross-protocol
attack.
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EXAMPLE: In the example above, /spaces_1/ would be 4 and
/spaces_2/ would be 10.
6. If /key-number_1/ is not an integral multiple of /spaces_1/,
then abort the WebSocket connection.
If /key-number_2/ is not an integral multiple of /spaces_2/,
then abort the WebSocket connection.
NOTE: This can only happen if the client is not a conforming
WebSocket client.
7. Let /part_1/ be /key-number_1/ divided by /spaces_1/.
Let /part_2/ be /key-number_2/ divided by /spaces_2/.
EXAMPLE: In the example above, /part_1/ would be 906,585,445 and
/part_2/ would be 179,922,739.
8. Let /challenge/ be the concatenation of /part_1/, expressed as a
big-endian 32 bit integer, /part_2/, expressed as a big-endian
32 bit integer, and the eight bytes of /key_3/ in the order they
were sent on the wire.
EXAMPLE: In the example above, this would be the 16 bytes 0x36
0x09 0x65 0x65 0x0A 0xB9 0x67 0x33 0x57 0x6A 0x4E 0x7D 0x7C 0x4D
0x28 0x36.
9. Let /response/ be the MD5 fingerprint of /challenge/ as a big-
endian 128 bit string. [RFC1321]
EXAMPLE: In the example above, this would be the 16 bytes 0x6E
0x60 0x39 0x65 0x42 0x6B 0x39 0x7A 0x24 0x52 0x38 0x70 0x4F 0x74
0x56 0x62, or "n`9eBk9z$R8pOtVb" in UTF-8.
10. Send the following line, terminated by the two characters U+000D
CARRIAGE RETURN and U+000A LINE FEED (CRLF) and encoded as
UTF-8, to the client:
HTTP/1.1 101 WebSocket Protocol Handshake
This line may be sent differently if necessary, but must match
the Status-Line production defined in the HTTP specification,
with the Status-Code having the value 101.
11. Send the following fields to the client. Each field must be
sent as a line consisting of the field name, which must be an
ASCII case-insensitive match for the field name in the list
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below, followed by a U+003A COLON character (:) and a U+0020
SPACE character, followed by the field value as specified in the
list below, followed by the two characters U+000D CARRIAGE
RETURN and U+000A LINE FEED (CRLF). The lines must be encoded
as UTF-8. The lines may be sent in any order.
|Upgrade|
The value must be the string "WebSocket".
|Connection|
The value must be the string "Upgrade".
|Sec-WebSocket-Location|
The value must be /location/
|Sec-WebSocket-Origin|
The value must be /origin/
|Sec-WebSocket-Protocol|
This field must be included if /subprotocol/ is not null, and
must not be included if /subprotocol/ is null.
If included, the value must be /subprotocol/
Optionally, include "Set-Cookie", "Set-Cookie2", or other
cookie-related fields, with values equal to the values that
would be used for the identically named HTTP headers. [RFC2109]
[RFC2965]
12. Send two bytes 0x0D 0x0A (UTF-8 CRLF).
13. Send /response/.
This completes the server's handshake. If the server finishes these
steps without aborting the WebSocket connection, and if the client
does not then fail the WebSocket connection, then the connection is
established and the server may begin sending and receiving data, as
described in the next section.
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Internet-Draft The WebSocket protocol October 20106. Error Handling6.1. Handling errors in UTF-8 from the server
When a client is to interpret a byte stream as UTF-8 but finds that
the byte stream is not in fact a valid UTF-8 stream, then any bytes
or sequences of bytes that are not valid UTF-8 sequences must be
interpreted as a U+FFFD REPLACEMENT CHARACTER.
6.2. Handling errors in UTF-8 from the client
When a server is to interpret a byte stream as UTF-8 but finds that
the byte stream is not in fact a valid UTF-8 stream, behavior is
undefined. A server could close the connection, convert invalid byte
sequences to U+FFFD REPLACEMENT CHARACTERs, store the data verbatim,
or perform application-specific processing. Subprotocols layered on
the WebSocket protocol might define specific behavior for servers.
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Internet-Draft The WebSocket protocol October 20107. Closing the connection7.1. Client-initiated closure
Certain algorithms require the user agent to *fail the WebSocket
connection*. To do so, the user agent must close the WebSocket
connection, and may report the problem to the user (which would be
especially useful for developers).
Except as indicated above or as specified by the application layer
(e.g. a script using the WebSocket API), user agents should not close
the connection.
User agents must not convey any failure information to scripts in a
way that would allow a script to distinguish the following
situations:
o A server whose host name could not be resolved.
o A server to which packets could not successfully be routed.
o A server that refused the connection on the specified port.
o A server that did not complete the opening handshake (e.g. because
it was not a WebSocket server).
o A WebSocket server that sent a correct opening handshake, but that
specified options that caused the client to drop the connection
(e.g. the server specified an origin that differed from the
script's).
o A WebSocket server that abruptly closed the connection after
successfully completing the opening handshake.
7.2. Server-initiated closure
Certain algorithms require or recommend that the server *abort the
WebSocket connection* during the opening handshake. To do so, the
server must simply close the WebSocket connection.
7.3. Closure
To *close the WebSocket connection*, the user agent or server must
close the TCP connection, using whatever mechanism possible (e.g.
either the TCP RST or FIN mechanisms). When a user agent notices
that the server has closed its connection, it must immediately close
its side of the connection also. Whether the user agent or the
server closes the connection first, it is said that the *WebSocket
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connection is closed*. If the connection was closed after the client
finished the WebSocket closing handshake, then the WebSocket
connection is said to have been closed _cleanly_.
Servers may close the WebSocket connection whenever desired. User
agents should not close the WebSocket connection arbitrarily.
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Internet-Draft The WebSocket protocol October 20108. Known extensions
Extensions provide a mechanism for implementations to opt-in to
additional protocol features. This section defines the meaning of
well-known extensions but implementations may use extensions defined
separately as well.
8.1. Compression
The registered extension token for this compression extension is
"deflate-stream".
The extension does not have any per message extension data and it
does not define the use of any WebSocket reserved bits or op codes.
Senders using this extension MUST apply RFC 1951 encodings to all
bytes of the data stream following the handshake including both data
and control messages. The data stream MAY include multiple blocks of
both compressed and uncompressed types as defined by RFC 1951.
[RFC1951]
Senders MUST NOT delay the transmission of any portion of a WebSocket
message because the deflate encoding of the message does not end on a
byte boundary. The encodings for adjacent messages MAY appear in the
same byte if no delay in transmission is occurred by doing so.
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Internet-Draft The WebSocket protocol October 20109. Security considerations
While this protocol is intended to be used by scripts in Web pages,
it can also be used directly by hosts. Such hosts are acting on
their own behalf, and can therefore send fake "Origin" fields,
misleading the server. Servers should therefore be careful about
assuming that they are talking directly to scripts from known
origins, and must consider that they might be accessed in unexpected
ways. In particular, a server should not trust that any input is
valid.
EXAMPLE: For example, if the server uses input as part of SQL
queries, all input text should be escaped before being passed to the
SQL server, lest the server be susceptible to SQL injection.
Servers that are not intended to process input from any Web page but
only for certain sites should verify the "Origin" field is an origin
they expect, and should only respond with the corresponding "Sec-
WebSocket-Origin" if it is an accepted origin. Servers that only
accept input from one origin can just send back that value in the
"Sec-WebSocket-Origin" field, without bothering to check the client's
value.
If at any time a server is faced with data that it does not
understand, or that violates some criteria by which the server
determines safety of input, or when the server sees a handshake that
does not correspond to the values the server is expecting (e.g.
incorrect path or origin), the server should just disconnect. It is
always safe to disconnect.
The biggest security risk when sending text data using this protocol
is sending data using the wrong encoding. If an attacker can trick
the server into sending data encoded as ISO-8859-1 verbatim (for
instance), rather than encoded as UTF-8, then the attacker could
inject arbitrary frames into the data stream.
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Internet-Draft The WebSocket protocol October 201010. IANA considerations10.1. Registration of ws: scheme
A |ws:| URL identifies a WebSocket server and resource name.
URI scheme name.
ws
Status.
Permanent.
URI scheme syntax.
In ABNF terms using the terminals from the URI specifications:
[RFC5234] [RFC3986]
"ws" ":" hier-part [ "?" query ]
The path and query components form the resource name sent to the
server to identify the kind of service desired. Other components
have the meanings described in RFC3986.
URI scheme semantics.
The only operation for this scheme is to open a connection using
the WebSocket protocol.
Encoding considerations.
Characters in the host component that are excluded by the syntax
defined above must be converted from Unicode to ASCII by applying
the IDNA ToASCII algorithm to the Unicode host name, with both the
AllowUnassigned and UseSTD3ASCIIRules flags set, and using the
result of this algorithm as the host in the URI. [RFC3490]
Characters in other components that are excluded by the syntax
defined above must be converted from Unicode to ASCII by first
encoding the characters as UTF-8 and then replacing the
corresponding bytes using their percent-encoded form as defined in
the URI and IRI specification. [RFC3986] [RFC3987]
Applications/protocols that use this URI scheme name.
WebSocket protocol.
Interoperability considerations.
None.
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Security considerations.
See "Security considerations" section above.
Contact.
Ian Hickson <ian@hixie.ch>
Author/Change controller.
Ian Hickson <ian@hixie.ch>
References.
This document.
10.2. Registration of wss: scheme
A |wss:| URL identifies a WebSocket server and resource name, and
indicates that traffic over that connection is to be encrypted.
URI scheme name.
wss
Status.
Permanent.
URI scheme syntax.
In ABNF terms using the terminals from the URI specifications:
[RFC5234] [RFC3986]
"wss" ":" hier-part [ "?" query ]
The path and query components form the resource name sent to the
server to identify the kind of service desired. Other components
have the meanings described in RFC3986.
URI scheme semantics.
The only operation for this scheme is to open a connection using
the WebSocket protocol, encrypted using TLS.
Encoding considerations.
Characters in the host component that are excluded by the syntax
defined above must be converted from Unicode to ASCII by applying
the IDNA ToASCII algorithm to the Unicode host name, with both the
AllowUnassigned and UseSTD3ASCIIRules flags set, and using the
result of this algorithm as the host in the URI. [RFC3490]
Characters in other components that are excluded by the syntax
defined above must be converted from Unicode to ASCII by first
encoding the characters as UTF-8 and then replacing the
corresponding bytes using their percent-encoded form as defined in
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Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
Header field name
Sec-WebSocket-Key2
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Key1| and |Sec-WebSocket-Key2| headers are used in
the WebSocket handshake. They are sent from the client to the server
to provide part of the information used by the server to prove that
it received a valid WebSocket handshake. This helps ensure that the
server does not accept connections from non-Web-Socket clients (e.g.
HTTP clients) that are being abused to send data to unsuspecting
WebSocket servers.
10.5. Sec-WebSocket-Location
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Location
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Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Location| header is used in the WebSocket
handshake. It is sent from the server to the client to confirm the
URL of the connection. This enables the client to verify that the
connection was established to the right server, port, and path,
instead of relying on the server to verify that the requested host,
port, and path are correct.
10.6. Sec-WebSocket-Origin
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Origin
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Origin| header is used in the WebSocket handshake.
It is sent from the server to the client to confirm the origin of the
script that opened the connection. This enables user agents to
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verify that the server is willing to serve the script that opened the
connection.
10.7. Sec-WebSocket-Protocol
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Protocol
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Protocol| header is used in the WebSocket
handshake. It is sent from the client to the server and back from
the server to the client to confirm the subprotocol of the
connection. This enables scripts to both select a subprotocol and be
sure that the server agreed to serve that subprotocol.
10.8. Sec-WebSocket-Draft
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Draft
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
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Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Draft| header is used in the WebSocket handshake.
It is sent from the client to the server to indicate the draft
protocol version of the connection. This enables servers to
correctly interpret the handshake and subsequent data being sent from
the data, and close the connection if the server cannot interpret
that data in a safe manner.
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Internet-Draft The WebSocket protocol October 201011. Using the WebSocket protocol from other specifications
The WebSocket protocol is intended to be used by another
specification to provide a generic mechanism for dynamic author-
defined content, e.g. in a specification defining a scripted API.
Such a specification first needs to "establish a WebSocket
connection", providing that algorithm with:
o The destination, consisting of a /host/ and a /port/.
o A /resource name/, which allows for multiple services to be
identified at one host and port.
o A /secure/ flag, which is true if the connection is to be
encrypted, and false otherwise.
o An ASCII serialization of an origin that is being made responsible
for the connection. [ORIGIN]
o Optionally a string identifying a protocol that is to be layered
over the WebSocket connection.
The /host/, /port/, /resource name/, and /secure/ flag are usually
obtained from a URL using the steps to parse a WebSocket URL's
components. These steps fail if the URL does not specify a
WebSocket.
If a connection can be established, then it is said that the
"WebSocket connection is established".
If at any time the connection is to be closed, then the specification
needs to use the "close the WebSocket connection" algorithm.
When the connection is closed, for any reason including failure to
establish the connection in the first place, it is said that the
"WebSocket connection is closed".
While a connection is open, the specification will need to handle the
cases when "a WebSocket message has been received" with text /data/.
To send some text /data/ to an open connection, the specification
needs to "send /data/ using the WebSocket".
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Internet-Draft The WebSocket protocol October 201012. Acknowledgements
Special thanks are due to Ian Hickson, who was the original author
and editor of this protocol. The initial design of this
specification benefitted from the participation of many people in the
WHATWG and WHATWG mailing list. Contributions to that specification
are not tracked by section, but a list of all who contributed to that
specification is given in the WHATWG HTML specification. [HTML]
Special thanks also to John Tamplin for providing a significant
amount of text for the Data Framing section of this specification.
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